In a recent study posted to the medRxiv* preprint server, researchers examined the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) booster doses in preventing severe SARS-CoV-2 Omicron infection outcomes.
Study: Effectiveness of mRNA COVID-19 monovalent and bivalent vaccine booster doses against Omicron severe outcomes among adults aged ≥50 years in Ontario, Canada. Image Credit: WirestockCreators/Shutterstock.com
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Background
Health Canada has approved the Moderna Spikevax® bivalent coronavirus disease 2019 (COVID-19) vaccine as a booster dose for adults aged 18 years and above. The vaccine targets both the original SARS-CoV-2 strain and the SARS-CoV-2 Omicron BA.1 sublineage.
The Pfizer-BioNTech Comirnaty® vaccine has been approved as a booster dose for persons aged 12 years and above. The vaccine targets both the original strain and Omicron BA.4/BA.5.
Previous research has shown that monovalent COVID-19 messenger ribonucleic acid (mRNA) vaccines effectively protect older adults in Canada against severe Omicron-related outcomes, although there is some evidence of decreased protection over time. However, the efficacy of bivalent COVID-19 vaccines has not yet been fully investigated.
About the study
In the present study, researchers compared the vaccine effectiveness (VE) of bivalent mRNA SARS-CoV-2 booster vaccines to that of monovalent mRNA vaccines in preventing severe SARS-CoV-2 Omicron-related outcomes.
A study was conducted on community-dwelling adults aged 50 years or older with at least one SARS-CoV-2 real-time polymerase chain reaction (PCR) test performed between 19 June 2022 and 28 January 2023.
Data were obtained from various datasets, including provincial SARS-CoV-2 laboratory testing, COVID-19 vaccination, health administrative data, and COVID-19 surveillance. These datasets were linked with unique encoded identifiers and assessed at Institute for Clinical Evaluative Sciences (ICES).
Adults who reported being vaccinated with two or more monovalent booster doses were assumed to have more similarities with those who presented for a bivalent booster dose. The team defined sublineage-predominant periods as over 50% of the sequenced samples from the province belonging to a particular sublineage.
Omicron BA.4/BA.5 was the main sublineage between 19 June 2022 and 3 December 2022, while BQ was predominant from 4 December 2022 to 28 January 2023.
The study evaluated the VE associated with Moderna monovalent (mRNA-1273), mRNA-1273 BA.1 bivalent, Pfizer-BioNTech monovalent (BNT162b2), and BNT162b2 BA.4/BA.5 bivalent booster doses in preventing severe outcomes in comparison to unvaccinated persons, based on the time since vaccination.
Results
The study analyzed 3,755 Omicron infection cases and 14,338 test-negative controls. The cases were older compared to the controls. Most cases and controls, around 57% and 69%, respectively, reported their most recent vaccination as the fourth dose.
Between 19 June and 11 September 2022, most adults received either the 33% of adults received mRNA-1273 monovalent while 66% received the BNT1262 monovalent vaccine as their most recent dose.
The most recent vaccine doses administered from 12 September 2022 onwards were mRNA-1273 monovalent, BNT162b2 monovalent, mRNA-1273 BA.1 bivalent, and BNT162b2 BA.4/BA.5 bivalent, received by 16%, 18%, 31%, and 35% of recipients, respectively.
Across the full study period, the VE of the mRNA-1273 monovalent vaccine was 85%, while that of the BNT162b2 monovalent vaccine was 88% around seven to 29 days post-vaccination. The mRNA-1273 and BNT162b2 monovalent vaccines showed 82% and 82% VE approximately 90 to 119 days after vaccination, respectively.
On the other hand, the mRNA-1273 BA.1 bivalent vaccine showed a VE of 86% between seven and 29 days post-vaccination and 76% between 90 and 119 days post-vaccination. The BNT162b2 BA.4/BA.5 bivalent vaccine showed a VE of 83% between seven and 29 days post-vaccination and 81% between 60 and 89 days post-vaccination.
During the BA.4/BA.5-predominant period, VE was slightly higher than the BQ-predominant period. The VE of the mRNA-1273 BA.1 bivalent vaccine and BNT162b2 BA.4/BA.5 bivalent vaccine were 93% and 87% between 30 and 59 days post-vaccination when BA.4/BA.5 was the predominant strain, respectively. During the BQ-predominant phase, the corresponding estimates were 82% and 82% for both vaccines.
Conclusion
The study findings showed that the monovalent and bivalent mRNA SARS-CoV-2 vaccines offer equal and effective initial protection against COVID-19-related hospitalization or mortality among adults aged 50 years and above.
Furthermore, monovalent and bivalent COVID-19 mRNA vaccines offer similar levels of initial protection against Omicron-related severe outcomes in adults aged 50 years and above.
Additional vaccine doses would benefit older adults the most as they experience the highest rates of severe outcomes related to COVID-19. Further research is required to establish bivalent vaccines’ durability and efficacy against emerging Omicron subvariants like XBB.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
